1. Field of the Invention
The present invention relates to a novel catalyst for the treatment/purification of industrial gases containing contaminating amounts of sulfur compounds.
As utilized herein, by the term "treatment of sulfur compounds" is intended any catalytic conversion of sulfur compounds contained in residual industrial gases into readily removable compounds.
This invention especially relates to a novel catalyst based on zirconium dioxide and use thereof in the Claus catalysis for the recovery of sulfur from residual gases comprising, in particular, hydrogen sulfide, sulfur dioxide and possibly organic sulfur derivatives, such as CS.sub.2 and COS.
2. Description of the Prior Art
In the conventional Claus process (to which the present invention is not limited), the recovery of sulfur from a gas containing hydrogen sulfide and possibly organic sulfur derivatives, includes two stages:
In a first stage, the hydrogen sulfide is burned in the presence of a controlled amount of air to convert a portion of the gas into sulfur dioxide, and in a second stage, the gaseous mixture thus produced is charged into reactors connected in series and containing a catalyst, in which the following reaction takes place: ##STR1##
In addition to hydrogen sulfide, the Claus gases may contain carbon compounds of sulfur, such as COS and CS.sub.2, which are generally relatively stable and resistant to catalytic conversion, and which contribute to an increase of 20 to 50% in the emission of SO.sub.2 and sulfur compounds into the atmosphere, following incineration of the fumes. These problematical compounds are either already contained in the gas to be treated, or are formed at high temperatures during the first stage.
These compounds may be eliminated by several types of reactions, in particular by hydrolysis according to the reactions (2), (3) and/or (4): EQU CS.sub.2 +2H.sub.2 O.fwdarw.CO.sub.2 +2H.sub.2 S (2) EQU CS.sub.2 +H.sub.2 O.fwdarw.COS+H.sub.2 S (3) EQU COS+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 S (4)
It has long been known to this art that alumina can be used as a catalyst for such types of reaction. However, alumina is only moderately effective for the elimination of those organic sulfur compounds noted above.
More recently, titanium dioxide has been used as a catalyst for such purpose: it displays catalytic activity clearly superior to that of alumina for the elimination of organic sulfur compounds. However, TiO.sub.2 has a mediocre initial activity at short contact times.